Isotherm Fridge

[emnick]

I have an Isotherm fridge (I think Danfoss compressor) that is not cutting out. It freezes all OK and also if anything is placed near the plate then that will freeze also.

I need to know how to test the capillary that goes into the thermostat adjuster. Can I presume that this opens or closes a contact on C&T of the compressor. There is a small resistor I think its for a compressed speed control??

As a short term fix I was going to install a small timer to turn fridge on / off every 20 mins or so . across the C & T terminals, Would this cause damage ?

At the moment the compressor is running very hot so we are just turning on and off. Not on shore power at moment so its also draining the batteries quickly.

Thanks for any help

 

[emnick]

Forgot to say that it is water cooled. Also could I just but a 12v digital thermostat to replace the existing if its defective that is??

 

[superheat6k]

It sounds like you are developing a solution for the symptoms, but not the problem.

Running hot and excessively suggests loss of refrigerant. As you will see from another thread on here, there there is no easy fix if it has lost its gas / leaked.

However, a small leak can be found by using a strong solution of fairy liquid around the various pipework and heat exchangers. Spay it on then look for a fine foaming where a leak may exist.

A clue to correct gas charge is the temperature of the suction pipe at the compressor. For a fridge this should be cool enough to form droplets of condensate. Above say 10oC then likely not enough gas, even if the evaporator plate forms a frost.

 

[GHA]

I need to know how to test the capillary that goes into the thermostat adjuster. Can I presume that this opens or closes a contact on C&T of the compressor. There is a small resistor I think its for a compressed speed control??

Yes, the thermostat is just a switch across c & t, and yes the resister is compressor speed control - no resistor is full speed.

Mine went ages ago, too long to remember the exact symptoms apart from warm beer does the thermostat still make a clicking sound when you turn the knob up and down? Will that turn the compressor on & off?

 

[jimmy_the_builder]

I have an Isotherm fridge (I think Danfoss compressor) that is not cutting out. It freezes all OK and also if anything is placed near the plate then that will freeze also.

I need to know how to test the capillary that goes into the thermostat adjuster. Can I presume that this opens or closes a contact on C&T of the compressor. There is a small resistor I think its for a compressed speed control??

As a short term fix I was going to install a small timer to turn fridge on / off every 20 mins or so . across the C & T terminals, Would this cause damage ?

At the moment the compressor is running very hot so we are just turning on and off. Not on shore power at moment so its also draining the batteries quickly.

Thanks for any help

You don't say which model of fridge you've got but I have a Isotherm Cruise 130 fridge and this model tends to get through thermostats every couple of years, it's a known issue. What happens is the stat corrodes and basically shorts out. A tell tale is corrosion stains around the stat. I believe, although I don't yet know this for sure, that the root cause is the hole in the insulation to route the cable for the stat isn't closed, so condensation forms in the stat itself drawn in from the warm outside air. So for this particular scenario, the solution is to replace the stat, and then seal up the cable hole.

 

[Trundlebug]

FWIW I can recommend fitting the digital thermostat, which comes complete with the smart energy control system that webasto / Isotherm have for this range of fridges.
I fitted it to mine from new and haven't regretted it.

It senses supply voltage and can therefore tell when power is plentiful (mains or engine running) or not (battery only), and will cool the contents down to about 1 degC to use them as a cold store and save energy when running off battery alone.
Doesn't sound much, but they reckon it saves around 30% which is significant.
As part of this system it also soft starts the compressor, which should improve life and reliability but also reduces noise.
https://www.webasto.com/int/markets...refrigeration-solutions/smart-energy-control/

 

[emnick]

Thanks I had considered this but the fridge is freezing everything in it....well if stored under the plate and it freezes really quickly in the freezer box so not so sure its low on gas. Most research suggests thermostat.

 

[emnick]

Yes, the thermostat is just a switch across c & t, and yes the resister is compressor speed control - no resistor is full speed.

Mine went ages ago, too long to remember the exact symptoms apart from warm beer does the thermostat still make a clicking sound when you turn the knob up and down? Will that turn the compressor on & off?

Yes will turn off and still makes a clicking sound.

Thanks

 

[emnick]

FWIW I can recommend fitting the digital thermostat, which comes complete with the smart energy control system that webasto / Isotherm have for this range of fridges.
I fitted it to mine from new and haven't regretted it.

This sounds interesting will have a look. Anybody fitted a 12v digital thermostat as found on eBay? etc

It senses supply voltage and can therefore tell when power is plentiful (mains or engine running) or not (battery only), and will cool the contents down to about 1 degC to use them as a cold store and save energy when running off battery alone.
Doesn't sound much, but they reckon it saves around 30% which is significant.
As part of this system it also soft starts the compressor, which should improve life and reliability but also reduces noise.
https://www.webasto.com/int/markets...refrigeration-solutions/smart-energy-control/

 

[Adethefridge]

When a system is low on refrigerant the evaporator is only partially frozen with the end of the evaporator loosing frost first, the thermostat phial is normally attached to the evaporator at this point so although 90% of the evaporator is frozen the section the phial is attached to isn't getting cold enough to cut out,
Check if the entire evaporator is freezing wetting your finger and seeing if it sticks will determine if liquid refrigerant is present at the end of the evaporator if so I suspect the thermostat is faulty
If liquid refrigerant isn't present at the end of the evaporator then it's probably low on refrigerant
Thermostats are very cheep £10/£15 but you must buy the correct type danfoss/ranco both have approx 10 stats they look identical but the range is different

 

[GHA]

Yes will turn off and still makes a clicking sound.

Thanks

If the thermostat can be forced to control the compressor but won't do so on it's own then it does sound like it's at fault here, no?

 

[emnick]

When a system is low on refrigerant the evaporator is only partially frozen with the end of the evaporator loosing frost first, the thermostat phial is normally attached to the evaporator at this point so although 90% of the evaporator is frozen the section the phial is attached to isn't getting cold enough to cut out,
Check if the entire evaporator is freezing wetting your finger and seeing if it sticks will determine if liquid refrigerant is present at the end of the evaporator if so I suspect the thermostat is faulty
If liquid refrigerant isn't present at the end of the evaporator then it's probably low on refrigerant
Thermostats are very cheep £10/£15 but you must buy the correct type danfoss/ranco both have approx 10 stats they look identical but the range is different

Thanks for reply. I just checked and the evaporator is freezing to touch all over. The small sensor that is at the end of the capillary tube is at the very front of the plate attached with a small steel clip so I can't move it anywhere else. I have been listening and the motor is running constantly for at least the last two hours. I was considering buying a digital one as it would appear that it opens / closes a contact is there a reason to replace like for like?

Thanks again for your help

 

[Adethefridge]

Your existing thermostat regulates the temperature of the evap not the fridge itself, if yours is a back plate evap the thermostat also controls the auto defrost function something like this
Cut out temperature -20°c to -28°c ( evap temp not fridge temp )
Fixed cut in temp +9°c
So once the thermostat has cut out it won't cut the compressor back in untill the evap has reached +9°c to ensure any ice has melted
like for like replacement : 10 mins work + £10 thermostat
Electronic thermostat : where to position the sensor air temperature or evap temperature ? How to control the auto-defrost?
Where to position the new controller
It can be done but requires a lot more thought and work....

 

[Adethefridge]

Correction..
both danfoss and ranco auto defrost thermostat have a cut- in temp of + 4.5°c
If you go for an electronic thermostat make sure it has a timed defrost function

 

[emnick]

Your existing thermostat regulates the temperature of the evap not the fridge itself, if yours is a back plate evap the thermostat also controls the auto defrost function something like this
Cut out temperature -20°c to -28°c ( evap temp not fridge temp )
Fixed cut in temp +9°c
So once the thermostat has cut out it won't cut the compressor back in untill the evap has reached +9°c to ensure any ice has melted
like for like replacement : 10 mins work + £10 thermostat
Electronic thermostat : where to position the sensor air temperature or evap temperature ? How to control the auto-defrost?
Where to position the new controller
It can be done but requires a lot more thought and work....

Many thanks for your prompt reply. never as simple as first thoughts ! I will look for a like for like.
Thanks again

 

[charles_reed]

Yes will turn off and still makes a clicking sound.

Thanks

Mine has in the past, refused to turn off. The capillary is available from Indel Webasto, for about €28.
I now carry spares of the 2 control wires are the two (red & black) "smart" boxes.

www.indelwebastomarine.com

Until you can fit the new thermostat (it plugs into the red box), I'd suggest controlling the unit on "manual" using a thermometer in the box to check temperature.
If it clicks on and off, part way round, the thermostat is still operative and possibly defrosting will sort out your problem?
The problem you describe certainly is not due to low refrigerant and if the thermostat is still working in manual mode it's down to a malfunctioning red box, which forgets to turn off the supercool function when system volts drop from a fully charged situation.
You're slightly overcooled if your fridge is freezing beer - mine only did that with a Freon 12 unit, long since replaced with modern refrigerant (unless it's very weak beer).